We've written frequently about building-integrated photovoltaics (BIPV), the concept of putting solar power generation capabilities into building materials, rather than as bolt-on additions. While we imagine the potential of "spray-on" photovoltaics to turn every sun-facing surface into a power source, the most common manifestation of BIPV has been "solar shingles" for home rooftops. Now comes word (via Inhabitat and Treehugger) of another BIPV concept, "Power Glass." Manufactured by San Diego-area company XsunX, Power Glass puts a transparent, thin-film polymer photovoltaic layer onto window glass.
According to XsunX, the thin-film polymer pv is suitable for "window, display, roof, canopy, and exterior façade applications." At least, they think so -- they haven't yet started shipping or licensing products, although they expect to do so soon. And they do appear to be getting close; earlier this month, they announced a process for creating "large area" sheets of thin-film pv, a necessary step for coating glass cost-effectively.
The Power Glass won't really replace standard solar panels for serious applications, however. Despite press material proclaiming "estimates of Power Glass solar cells operating at as much as 50%, or half, the efficiency of conventional opaque amorphous solar cells yet costing as little as 25%, or one fourth, to produce," the fine print on the site shows that their current processes make pv materials with around 4% conversion efficiency, with the possibility of 6%. 4-6% efficiency shouldn't be dismissed as meaningless, of course; on buildings with abundant window space, the power output from even low-efficiency pv could be substantial (a tall building with good sun visibility might even see tens of kilowatts of peak power).
Eventually, the cost, efficiency and convenience of use curves will intersect for a wide variety of material objects. Already, building-integrated photovoltaics can make a great deal of sense, as most buildings have some access to sunlight and can balance their power generation and demand through connection to the grid. As polymer photovoltaic costs come down and efficiency increases, we're likely to see at least experimental integration into the bodies of hybrid vehicles. This will be limited initially, as cars are less likely to spend as much time in the sun as buildings, and (because of the way cars are curved) will have a smaller proportion of their surface area receiving full sunlight at any given time.
Even wider use of object-integrated pv is possible with much greater efficiency and much lower cost. One scenario -- by no means the most likely, but certainly conceivable -- has thin-film photovoltaic coatings on most objects, whether or not they receive abundant sunlight, as long as they can store the resulting trickle of power or are connected to the grid. This would be the ultimate form of distributed power generation. A more plausible version of that scenario, and one which would be more readily achievable in the near-term, would have photovoltaic layers on most large-area outside surfaces, including billboards, freeway sound walls, and parking lot structures. That these examples are all aspects of a car culture is quite intentional; this could be a way for the automobile infrastructure to help reduce society's overall footprint.
For the present, building-integrated solar is the most realistic pathway for increased photovoltaic use. I'd like to see greater incentives for its adoption, such as a BIPV-specific "green mortgage" or some kind of tax rebate or credit. At the very least, I would encourage the owners of buildings with solar power features to put out some kind of public notice of how much power the building has generated and how much money this has saved. If you're going to contribute to the Bright Green Future, you should at least be allowed to brag a little.
How about on the exteriors of autos to supplement the power generation within?
I like it. Never having to worry about your car's battery going dead- people pay to have booster cables in the car at all times, or solar panels that recharge the batteries so it won't be flat after a holiday.
Hmm... come to think of it, these solar panels are going to have lots of weird uses that go beyond just power generation. Even if it's not cost-effective per kWh or as a fuel-efficiency measure, a guarantee that your battery will never run out still seem like a valuable feature.
Look at that window!
That's not just a tint, it is
Unfortunately, a car with PV windows could still have its battery go dead. All it would take is two weeks in an airport parking lot under an inch of snow. ;-)
If someone manages to make a conformal plastic PV cell using quantum dots (up to 65% efficiency is the figure being bandied about) the hood, roof and other surfaces could generate enough energy to be useful as motive power for a plug-in hybrid.
I would like to clarify some information presented in this article regarding the efficiency of Power Glass. The article mentions that XSunX's Power Glass website states "in the fine print" that 4-6% efficiancy is achieved. But common manufacturing methods produce traditional opaque amorphous solar cells with an efficiency of 12-15% when converting sunlight to electricity. So an efficiancy of Power Glass *IS* about 50% that of standard solar cells (4-6% is about half of 12-15%).
Looks like 1/3 to 40% to me. Claiming 50% isn't being honest.
10 square meters of solarium roof with this stuff looks like it would give about 500 watts in full sun (figuring 5%). The glass fronting a 12-foot wide tower office, perhaps 300-400 watts peak depending on sun elevation. That doesn't need exaggerating.